A wide variety of hormones, neurotransmitters, and other biologically active substances control, regulate, or adjust the functions of the body via interaction with specific cellular receptors. Many of these receptors mediate the transmission of intracellular signals by activating guanine nucleotide-binding proteins (G proteins) to which the receptor is coupled. Such receptors are generically referred to as G-protein coupled receptors (GPCRs) and include, among others, adrenergic receptors, opioid receptors, cannabinoid receptors, and prostaglandin receptors. The biological effects of activating these receptors are not direct but are mediated by a host of intracellular proteins. The importance of these secondary proteins has only recently been recognized and investigated as intervention points in disease states. One of the most important classes of downstream effectors is the “kinase” class.
Various kinases play important roles in the regulation of many physiological functions. For example, kinases have been implicated in numerous disease states including, but not limited to, cardiac disorders such as angina pectoris, essential hypertension, myocardial infarction, supraventricular and ventricular arrhythmias, congestive heart failure, and atherosclerosis, respiratory disorders such as asthma, chronic bronchitis, bronchospasm, emphysema, airway obstruction, rhinitis, and seasonal allergies, inflammation, rheumatoid arthritis, renal failure, and diabetes. Other conditions include chronic inflammatory bowel disease, glaucoma, hypergastrinemia, gastrointestinal indications such as acid/peptic disorder, erosive esophagitis, gastrointestinal hypersecretion, mastocytosis, gastrointestinal reflux, peptic ulcer, pain, obesity, bulimia nervosa, depression, obsessive-compulsive disorder, organ malformations (e.g., cardiac malformations), neurodegenerative diseases such as Parkinson's Disease and Alzheimer's Disease, multiple sclerosis, Epstein-Barr infection, and cancer (Nature Reviews Drug Discovery 2002, 1: 493-502). In other disease states, the role of kinases is only now becoming clear.
The success of the tyrosine-kinase inhibitor STI571 (Gleevec) in the treatment of chronic myelogenous leukemia (Nature Reviews Drug Discovery 2003, 2: 296-313) has spurred considerable efforts to develop other kinase inhibitors for the treatment of a wide range of other cancers (Nature Reviews Cancer 2003, 3: 650-665). Seven additional kinase inhibitor drugs have since been brought to market, establishing kinase inhibitors as an important new drug class. Currently more than 100 protein kinase inhibitors are in clinical development (Kinase Inhibitor Drugs 2009, Wiley Press).
In view of the role that kinases have in many disease states, there is an urgent and continuing need for small molecule ligands that inhibit or modulate the activity of kinases. Without wishing to be bound by theory, it is thought that modulation of the activity of kinases, including rho kinase (ROCK), by the compounds of the present invention is, in part, responsible for their beneficial effects.
An additional area of fruitful research in medicine is the study of monoamine transporters and the benefits of inhibition thereof. Monoamine transporters (MAT) are structures in cell membranes that transport monoamine-containing neurotransmitters into or out of cells. There are several distinct monoamine transporters, or MATs: the dopamine transporter (DAT), the norepinephrine transporter (NET), and the serotonin transporter (SERT). DAT, NET, and SERT are structurally-related, and each contains a structure of 12 trans-membrane helices. Modern antidepressants are thought to work by enhancing serotonergic, noradrenergic, or dopaminergic neurotransmission by binding to their respective transporter, and thereby inhibiting neurotransmitter reuptake and effectively raising the concentration of the neurotransmitter in synapses. Examples of drugs that are thought to operate by this mechanism include fluoxetine, a selective SERT inhibitor; reboxetine, a norepinephrine (NET) inhibitor; and bupropion, which inhibits both the NET and DAT (He, R. et al. J. Med. Chem. 2005, 48: 7970-9; Blough, B. E. et al. J. Med. Chem. 2002, 45: 4029-37; Blough, B. E., et al. J. Med. Chem. 1996, 39: 4027-35; Torres, G. E., et al. Nat. Rev. Neurosci. 2003, 4: 13-25).
Glaucoma causes deterioration of the eye's optic nerve, the nerve bundles that carry images from the ganglion cells of the eye to the brain. Increased IOP is a hallmark of the most common forms of glaucoma, and this increased intraocular pressure likely damages the optic nerve and ganglion cells through multiple mechanisms. Current glaucoma medications act by reducing intraocular pressure, either by slowing the flow of aqueous humor into the eye or by improving the drainage of this fluid from the eye. Inhibitors of rho kinase have been shown to reduce IOP in rabbits and monkeys by increasing aqueous humor drainage through the trabecular meshwork (Tian and Kaufman, Arch Ophthalmol 2004, 122: 1171-1178; Tokushige et al., IOVS 2007, 48(7): 3216-3222). Several lines of experimental evidence indicate that modulating the activity of rho kinase within the aqueous humor outflow pathway could be beneficial for the treatment of patients with glaucoma (Honjo et al., IOVS 2001; 42: 137-144; Waki et al., Curr Eye Res 2001; 22: 470-474; Rao et al., IOVS 2001; 42: 1029-1037). Considerable evidence suggests that the sympathetic nervous system plays a significant but complex role in the regulation of IOP (Nathanson, Proc. Natl. Acad. Sci. USA 1980; 77(12):7420-7424). Sympathetic nerve fibers innervate the ciliary process and trabecular meshwork (Ehinger, Acta Univ. Lund Sect 2 1964; 20:3-23; Sears, 1975, Handbook of Physiology, Endocrinology VI. Eds Astwood E & Greep R: 553-590) and both sympathetic stimulation and locally applied β-adrenergic agonists such as epinephrine decrease IOP (Sears, 1975, ibid; Dayson et al., J. Physiol. (London) 1951; 113:389-397).